In the field of packaging, whereby polymer films are used for covering or enclosing items of sale, and where film clarity or good optical properties are desired, there is a recognized need for polymer films which resist fogging when exposed to conditions of temperature and humidity which can produce condensation on the film. This condensation is especially troublesome when the interior of the package contains enough moisture to produce fogging of the interior surface of the film. Of special interest here is the packaging of food products, such as meats, bakery items, vegetables, fruits, and the like, though non-food items are also of interest.
Food products are often packaged in polymeric film for ease in handling by customers, to provide sanitary protection of the food product from the environment, to provide an easier and more economical wrapping than paper, or to provide a better view of the food product. Various polymeric materials such as polyvinyl chloride, poly(ethylene/vinyl acetate) and irradiated polyethylenes have been used in the food wrap market with plasticized polyvinyl chloride (PVC) being widely used in the market. Freshly cut meat and vegetables are often packaged in these films, and certain properties are desired of the film for it to perform satisfactorily as a food overwrap. Obviously, film used in this application should have good "see through" clarity so the product can be viewed. High gloss is desired to add "sparkle" to the packages for aesthetic appeal to the customers. As these food products are packaged, they generally experience a temperature change from where they are packaged to where they are stored or sold. This temperature change can cause the formation of water droplets on the inside surface of the film (commonly called "fog"). These water droplets are usually objectionable because they hinder the view of the food products from the consumer and can cause spoilage, particularly to certain vegetables. To prevent water from condensing in droplets, an antifog agent is often added to the film. The antifog agents reduce the surface tension of the water and cause the water to form a continuous sheet, which is then transparent.
Another desired property of the packaging film, to insure a neat package, is good film strength and handleability. Handleability is the ability of the film to stretch and conform to the shape of the food product being wrapped. The film must endure this stretching without puncturing or tearing. This film strength becomes even more important as meat packaging becomes automated. The film also should have enough cling to remain in place over the food product until the package is heat sealed. The film desirably is heat-sealable within the temperature range of the heat-sealers currently in use and provides a strong enough heat seal to retain excess blood and/or water which seeps from the food.
Not only should the package be aesthetically pleasing to the customers but the food product should also have a fresh appearance. This is particularly important for fresh red meat. Slaughtered meat is a deep maroon color and needs oxygen to convert the color of the meat to a bright red color ("bloom") as normally seen in markets. For the most to "bloom", the film used for wrapping must be highly permeable to oxygen. The meat tissue continues to use oxygen in the production of enzymes, so the oxygen permeability must be high enough to maintain the red color of the meat. Fresh red meat should maintain its red color for three to four days, depending on the cut of the meat, the temperature at which the meat has been stored, and the bacterial growth. Another aspect of preserving the appearance of the food product is preventing dehydration. The relative humidity of the refrigerator case is low due to the temperature at which meat is stored. Thus, the film used in wrapping should have a low water vapor permeability to prevent dehydration of the meat.
There is a perceived need in the market place for improved packaging films, especially for food products, most especially for red meat packaging, where the widely used plasticized polyvinylchloride (PVC) requires replacement by a more acceptable film. Much of the PVC which has been used is plasticized with additives, e.g. dioctyl phthalate, which are becoming less acceptable in the market.
U.S. Pat. No. 4,189,420 discloses, inter alia, certain ethylene polymers blended with a polybutene and a mixed glyceride having at least one acyl group of 2 to 6 carbon atoms and at least one acyl group containing 8 to 22 carbon atoms.
U.S. Pat. No. 3,048,266 discloses, inter alia, an anti-fog agent of polyethylene oxide derivative in a polyolefin composition.
U.S. Pat. No. 3,048,263 discloses, inter alia, a polyolefin anti-fog agent comprising a monoglyceride of a fatty acid.
U.S. Pat. No. 2,462,331 discloses, inter alia, the incorporation into polyethylene of polyhydric alcohol esters or metal salts of either saturated or unsaturated monocarboxylic fatty acids.